Picture reproduction apparatus and picture decoding apparatus

ABSTRACT

The picture reproduction apparatus of this invention reproduces compressed image data which has been compressed using inter-frame encoding, extracts a header from the reproduced image data, taking out intra-frame encoded image data using the information of the header. Invalid data is added to the image data other than the intra-frame encoded data. The image data is output into a picture decoding apparatus, so as to obtain a reproduced video image during playback in fast forward and fast reverse. Alternatively, valid image data is detected from the reproduced image data.

This application is a divisional of U.S. patent application Ser. No.08/807,640 filed Feb. 27, 1997, now U.S. Pat. No. 5,841,939, which is adivisional of U.S. patent application Ser. No. 08/254,037 filed Jun. 3,1994 and issued Jul. 15, 1997 as U.S. Pat. No. 5,649,047.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a picture reproduction apparatus and apicture decoding apparatus used for reproducing a digital compressedvideo image recorded on a recording medium.

2. Description of the Related Art

An apparatus for recording/reproducing a compressed digital video imagehas been developed with the progress of picture compression techniques.FIG. 18 is a block diagram of a conventional picturerecording/reproducing apparatus. The conventional picturerecording/reproducing apparatus shown in FIG. 18 includes a pictureencoding section 91 using an intra-frame discrete cosine transform (DCT)encoder, a recording section 92, a recording medium 93, a reproducingsection 94, and a picture decoding section 95 using an intra-frame DCTdecoder. A digital video image taken by a camera or the like is inputinto the intra-frame DCT encoder 91. In the intra-frame DCT encoder 91,the digital video image is encoded by data processing such as DCT andvariable length encoding, frame by frame. Then, the processed videosignal is rearranged into a recording format, and an error correctioncode is added thereto in the recording section 92. Thereafter, thereformatted digital video signal with the error correction code isrecorded onto the recording medium 93. During the playback, any error inthe reproduced signal is corrected, and the reproduced signal isreformatted into a decoding format in the reproducing section 94.Thereafter, the reproduced signal is decoded by a data process such asvariable length decoding and inverse DCT in the picture decoding section95, so as to obtain a reproduced video image. As to the intra-frameencoding, a usual encoding is completed in a data unit of one frame orone block consisting of (8×8) pixels or the like. Accordingly, duringplayback in fast forward or fast reverse in which only a part of datacan be reproduced, the resulting video image has a certain quality withwhich the contents of the image can be perceived (see, for example,"Study on Image Quality Reproduced at Variable Speeds by Digital VCR",by Takakura et al., Extended Abstracts; The Annual Meeting of TheInstitute of Television Engineers, 1992, pp. 93-94).

FIG. 19 is a block diagram of a conventional picture decoding apparatususing motion-compensation and inter-frame encoding techniques. In FIG.19, a picture decoding section 4 includes a buffer 41, a variable lengthdecoder 42, an inverse quantization circuit 43, an inverse DCT circuit44, and a motion compensating circuit 45. Also, a frame memory 5 isprovided. First, compressed image data is input into the buffer 41.Then, the data is decoded by processing of variable length decoding,inverse quantization, and inverse DCT, so as to obtain real-time data.In this scheme, the inter-frame decoding technique is used, so that thedifference between successive frames is encoded. Accordingly, when theimage data is to be recovered, the decoded difference data is added to ablock obtained by motion-compensating the data of previous frames storedin the frame memory 5 by each block, so as to obtain the decoded imagedata.

According to the inter-frame encoding by which the difference is sent, amotion component is effectively transmitted by motion compensation.Thus, the inter-frame encoding system can attain high data compressionrates while suppressing deterioration of image quality, as compared withthe intra-frame encoding system shown in FIG. 18 (see, for example,ISO/IEC/DIS 11172 "Information Technology--Coding of moving pictures andassociated audio for digital storage media up to about 1.5 Mbps", 1992,p. 61).

Since the system shown in FIG. 18 uses the intra-frame encoder, there isa disadvantage in that the data compressibility can not be set as highas that in the inter-frame encoding system or the like. Thisdisadvantage can be overcome by using an inter-frame encoding techniquein the picture encoding section and decoding section as in the systemshown in FIG. 19. However, the difference data is encoded, so that thecurrent frame can be reproduced only after the image of previous frameis reproduced. Thus, the system shown in FIG. 19 also has a disadvantagein that the desired image cannot be obtained during playback in fastforward or fast reverse in which only a part of the image data can bereproduced.

In slow playback at a half speed or the like, as shown in FIG. 20, theoutput from the reproducing section includes mixed reproduced image dataand other invalid data (cross talk, noise etc.) in a doubled period ascompared with normal playback. The kind of invalid data is not assured,so that a synchronization pattern or the like may possibly be output.Therefore, if the reproduced output is directly sent to the decodingapparatus, malfunctions of the decoding apparatus such as turbulence inthe reproduced image occurs due to the invalid data portion.

SUMMARY OF THE INVENTION

The picture reproduction apparatus of this invention includes:reproducing means for reproducing compressed image data from a recordingmedium, the compressed image data including an intra-frame encoded dataand a header having information for the intra-frame encoded data; headerextracting means for detecting and extracting the header from thereproduced image data; intra-frame encoded data extracting means forextracting the intra-frame encoded data from the reproduced image databy using the information of the extracted header; and invalid dataadding means for adding invalid data to the extracted intra-frameencoded data, thereby producing a trick-play compressed image data, andfor outputting the trick-play compressed image data into a picturedecoding apparatus during a trick-play mode.

In one embodiment of the invention, the picture reproduction apparatusmay further include recording means for receiving the compressed imagedata and for recording it onto the recording medium.

In another embodiment of the invention, the picture reproductionapparatus may further include switch means for, during a normalplayback, outputting the compressed data reproduced from the recordingmedium into the picture decoding apparatus, and for, only when atrick-play mode signal for requesting trick-play is input into theswitch means, outputting the trick-play compressed image data into thepicture decoding apparatus.

In another embodiment of the invention, only when a trick-play modesignal is input, a trick-play mode signal is output into the picturedecoding apparatus together with the trick-play image data.

In another embodiment of the invention, the invalid data includes aheader of remaining part of the compressed image data which cannot bereproduced.

According to another aspect of the invention, a picture decodingapparatus is provided. The picture decoding apparatus includes: picturedecoding means for decoding compressed image data; a frame memory forstoring the decoded image data; and trick-play control means for, when adecoding disable signal is input for a predetermined or longer period,performing a control so that an intra-frame encoded portion is extractedfrom the compressed image data and only the intra-frame encoded portionis written into the frame memory, and the contents for the remainingportion other than the intra-frame encoded portion are not updated.

Alternatively, the picture decoding apparatus may alternatively includestrick-play control means for, when a trick-play mode signal is input,performing a control so that only an intra-frame encoded portion isextracted from the decoded image data and written into the frame memory,and the contents for the remaining portion other than the intra-frameencoded portion are not updated.

According to another aspect of the invention, a picture reproductionapparatus is provided for reproducing compressed image data from arecording medium, and for outputting the image data reproduced from therecording medium into a picture decoding apparatus, frame by frame, inaccordance with either one of a normal playback mode or a slow playbackmode. The picture reproduction apparatus includes: reproducing means forreproducing the compressed image data from the recording medium, and foroutputting the reproduced image data including valid image data andinvalid image data; valid image data detecting means for detecting thevalid image data from the reproduced image data capable of beingrecovered of the image data or invalid image data having no relationshipwith the image data, and for generating a valid data detection signalidentifying the valid image data; invalid data producing means for, whenthe invalid image data is input, producing invalid data for a period inwhich the invalid image data is input; and trick-play control means for,in the normal playback mode, outputting the image data obtained from thereproducing means, and for, in the slow playback mode and when the validdata detection signal is input from the valid data detecting means,dividing the valid image data into variable-length encoded unit data,the unit being the minimum unit capable of being variable-lengthencoded, so as to alternately output the variable-length encoded unitdata of one unit or more and the invalid data.

According to another aspect of the invention, the picture reproductionapparatus may alternatively include trick-play control means for, in thenormal playback mode, outputting the image data obtained from thereproducing means, and for, in the slow playback mode at a 1/N speed (Nis a natural number) outputting one frame of the valid image data and(N-1) frames of the invalid data in a period equivalent to N frames inthe normal playback.

According to another aspect of the invention, the picture reproductionapparatus may alternatively include trick-play control means for, in thenormal playback mode, outputting the image data obtained from thereproducing means, and for, in the slow playback mode at a 1/N speed (Nis a natural number) storing M (M is a natural number) frames of thevalid image data obtained by the valid image data detecting means, so asto periodically output M frames of the valid image data and (N-1)×Mframes of the invalid data.

According to another aspect of the invention, the picture reproductionapparatus may alternatively include trick-play control means for, in thenormal playback mode, outputting the image data obtained from thereproducing means, and for, in the slow playback mode at a 1/N speed (Nis a natural number) storing the valid image data obtained by the validdata detecting means, and dividing the stored valid image data into Mframes, so as to repeatedly output each of the M frames N times.

In one embodiment of the invention, the picture reproduction apparatusmay further include recording means for receiving the compressed imagedata and for recording it onto the recording medium.

In another embodiment of the invention, the trick-play control meansoutputs the valid image data and the invalid data, and also outputs atrick-play mode signal including a slow playback ratio N, into thepicture decoding apparatus in the trick-play mode.

According to another aspect of the invention, a picture decodingapparatus is provided for decoding compressed image data output from apicture reproduction apparatus and reproducing valid image data ineither of a normal playback mode or a slow playback mode. The picturedecoding apparatus includes: picture decoding means for decoding thecompressed image data output from the picture reproduction apparatus; aframe memory for storing the image data decoded by the picture decodingmeans; and trick-play control means for performing a control so that aframe number is extracted from the reproduced image data, and, when theextracted frame number is the same as that of the image data which isinput immediately before, the image data which is the same as theprevious image data is again written into the frame memory.

According to another aspect of the invention, the picture decodingapparatus may alternatively include trick-play control means forperforming a control so that a frame number is extracted from thereproduced image data, and whether the extracted frame number is thesame as that of the image data which is input immediately before or notis determined, and performs a control so that, for the frame number ofthe image data which has been already decoded, the input image data isnot written into the frame memory.

According to another aspect of the invention, the picture decodingapparatus may alternatively include trick-play control means forperforming a control so that, when a time required for decoding oneframe of compressed image data is equal to (N-1) frames or more or equalto N frames or less (N is a natural number), the contents of the framememory are retained for a period of N frames or more.

According to another aspect of the invention, the picture decodingapparatus may alternatively include trick-play control means forperforming a control so that, when a slow playback mode at a 1/N speed(N is a natural number) is input, the contents of the frame memory areretained for a period of N frames or more.

According to the above construction, even when the compressed image datais encoded by inter-frame encoding, only the intra-frame encoded blockis extracted and sent to the decoding apparatus in which the update isperformed for the intra-frame encoded block. Thus, it is possible toobtain a reproduced picture during the trick play in fast forward orfast reverse. In addition, since the intra-frame encoded block isextracted by detecting only the header of the compressed data, it isunnecessary to decode all of the compressed image data during theplayback. Accordingly, even in the case where the inter-frame compresseddata is recorded on a recording/reproducing apparatus or the like whichutilizes the intra-frame encoding technique, the above function can berealized by adding a simple circuit.

Furthermore, the output of N frames from the picture reproductionapparatus is composed of valid data of one frame and invalid data of(N-1) frames, or the image data of one frame is held for N frames in thepicture decoding apparatus, so that the desired reproduced picture canbe obtained during slow playback at 1/N speed even in the cases wherethe compression is performed by inter-frame encoding.

Thus, the invention described herein makes possible the advantage ofproviding a picture reproduction apparatus and a picture decodingapparatus for allowing a picture to be reproduced during trick play suchas fast forward, fast reverse, or slow, even when the inter-frame codingis used.

This and other advantages of the present invention will become apparentto those skilled in the art upon reading and understanding the followingdetailed description with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a picture reproduction apparatus in a firstexample according to the invention.

FIG. 2 illustrates a format of compressed image data according to theinvention.

FIG. 3 illustrates a format of compressed image data according to theinvention.

FIG. 4 is a detailed block diagram of the picture reproduction apparatusin the first example according to the invention.

FIG. 5 illustrates a format of compressed image data for trick play inthe first example according to the invention.

FIG. 6 illustrates a format of compressed image data for trick play inthe first example according to the invention.

FIG. 7 is a block diagram of a picture reproduction apparatus in asecond example according to the invention.

FIG. 8 is a block diagram of a picture decoding apparatus in a thirdexample according to the invention.

FIG. 9 shows an algorithm illustrating the operation of the CPU in thethird example according to the invention.

FIG. 10 is a block diagram of a picture decoding apparatus in a fourthexample according to the invention.

FIG. 11 is a block diagram of a picture reproduction apparatus in afifth example according to the invention.

FIG. 12 shows an algorithm illustrating the operation of the CPU in thefifth example according to the invention.

FIGS. 13A through 13E illustrate outputs from the picture reproductionapparatus in the fifth example according to the invention.

FIG. 14 is a block diagram of a picture reproduction apparatus in asixth example according to the invention.

FIG. 15 is a block diagram of a picture decoding apparatus in a seventhexample according to the invention.

FIG. 16 shows an algorithm illustrating the operation of the CPU in theseventh example according to the invention.

FIG. 17 is a block diagram of a picture decoding apparatus in an eighthexample according to the invention.

FIG. 18 is a block diagram of a conventional picturerecording/reproducing apparatus.

FIG. 19 is a block diagram of a conventional picture decoding apparatus.

FIG. 20 illustrates outputs from a conventional picture reproductionapparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The entire disclosure of U.S. patent application Ser. No. 08/807,640filed Feb. 27, 1997 is expressly incorporated by reference herein. Thepresent invention will be described hereinafter by way of illustrativeexamples with reference to the accompanying drawings.

EXAMPLE 1

FIG. 1 is a block diagram of a picture reproduction apparatus in a firstexample according to the invention. In FIG. 1, the picture reproductionapparatus 1 includes a reproducing section 11, a header detectingsection 12, an intra-frame encoded block extracting section 13, and aninvalid data adding section 14. Also, a recording medium 2, a recordingsection 3, and a picture decoding apparatus 40 are provided. FIGS. 2 and3 are explanatory diagrams illustrating formats of the compressed data.FIG. 4 schematically shows the detailed construction of the headerdetecting section 12, the intra-frame encoded block extracting section13, and the invalid data adding section 14. FIGS. 5 and 6 illustrateexemplary formats of trick-play compressed image data 16.

The picture reproduction apparatus having the above construction isdescribed referring to FIGS. 1, 2, 3, 4, 5, and 6.

In FIG. 1, the input image data is assumed to be compressed byinter-frame encoding. The compressed image data is reformatted into arecording format and an error correction code is added thereto in therecording section 3, similar to the recording section 92 in theconventional example as shown in FIG. 18. Then, the reformatted imagedata with the error correction code is recorded onto the recordingmedium 2. During normal playback, any error in the reproduced signal iscorrected, and the reproduced signal is reformatted into a decodingformat in the reproducing section 11. Thereafter, the reproduced imagedata is sent out to the picture decoding apparatus 40.

FIGS. 2 and 3 illustrate exemplary data formats of compressed imagedata. In the inter-frame compression encoding method which is currentlygenerally used, one frame is split into blocks each having about 16×16pixels. Next, either of the inter-frame encoding in which the differencebetween frames is encoded, or the intra-frame encoding in which theoriginal data itself is encoded is selected by calculation, whicheverwill result in a smaller amount of information to be sent. Accordingly,the compressed data of one frame includes mixed inter-frame andintra-frame encoded data. As described above, in the trick play such asfast forward or fast reverse, only a part of the recorded data can bereproduced because a tape head cannot scan the whole tracks on arecording medium. Herein, data which is partially reproduced, that is tosay, data which cannot be variable-length decoded, is referred to as"invalid image data." Invalid image data is generated when a header or aterminating code of a data block is not read. If the reproduced part ofthe recorded data is the difference data, data to be added is required.However, there is no assurance that the data to be added is alsoreproduced.

In FIG. 2, intra-frame encoded blocks are collected immediately after aspecific header pattern. In this case, it is assumed that the headerpattern includes a flag indicating that the succeeding data includesinter-frame encoded blocks or that the succeeding data consists of onlyintra-frame encoded blocks. In FIG. 3, the data after a header patternincludes mixed inter-frame encoded blocks and intra-frame encodedblocks. In this case, it is assumed that the positions of theintra-frame encoded blocks are identified in the header pattern, forexample, using the number of bits measured from the header pattern, sothat the positions are determined without decoding.

Now, consider the case where image data having the formats shown inFIGS. 2 and 3 are recorded, and a trick-play mode signal 15 requiringthe trick play is input. The reproduced image data is first input intothe header detecting section 12. In the header detecting section 12, theheader pattern is compared with the contents of a read only memory (ROM)121 by a comparator 122. Thus, the header pattern is checked. Then, onlythe image data including any intra-frame encoded blocks after the headerpattern is sent to the intra-frame encoded block extracting section 13.In the intra-frame encoded block extracting section 13, a signalindicating the position of the intra-frame encoded block is generatedfrom the input data in a timing generator 132. The thus generated signalis fed into a gate 131, so that only the intra-frame encoded blocks areextracted from the image data and sent to the invalid data addingsection 14. In the invalid data adding section 14, the intra-frameencoded blocks are stored in a memory 141. In accordance with the timinggenerated by a timing generator 143, a selector 144 selectively outputsa header pattern stored in a ROM 142, intra-frame encoded data stored inthe memory 141, or an invalid data stored in the ROM 142 into thepicture decoding apparatus 40, as the trick-play compressed image data16. Herein, the term "invalid data" means data which is ignored by thedecoding apparatus. Invalid data is not decoded by the decodingapparatus and does not cause malfunction when decoding. FIG. 5 shows anexample of trick-play compressed image data 16. A header is addedimmediately before the extracted intra-frame encoded block, and in theremaining time period, the invalid data 0 is continuously output, inorder to prevent a pattern identical with the header pattern from beingdetected. In this example, the data output format is the same as that ofthe compressed image data. As to the header pattern, it is sufficient toadd a header at least for the picture decoding apparatus 40 to decodethe image data, such as a header of the intra-frame encoded block to bedecoded. It is not necessary to add headers to all of the blocks whichare not reproduced.

The picture decoding apparatus 40 receives the resulting output in whichthe invalid data is inserted into portions corresponding to theinter-frame encoded blocks. Accordingly, the portions cannot be decoded,so that the image data of the previous frame is retained. On the otherhand, the reproduced intra-frame encoded blocks can be properly decoded,so that only the intra-frame encoded blocks are updated.

According to the first example with the above-described construction,the picture reproduction apparatus 1 is only required to decode theheaders. During the trick play, a part of image is displayed, and hencethe contents of the displayed image can be recognized.

In the first example, the invalid data adding section 14 adds theinvalid data 0 to the trick-play compressed image data 16. However, theinvalid data is not limited to 0. For example, in the case where theheader pattern is established so that the picture decoding apparatus 40can detect the header pattern without failure, indeterminate data "x" asshown in FIG. 6 may be added. In general, the probability that suchindeterminate data will be decoded as the normal image data by thepicture decoding apparatus 40 is extremely low. Thus, there arises nopractical problem, if certain indeterminate data is added.

In the first example, only the intra-frame encoded blocks are extractedby the gate 131. Alternatively, if the reproduced header patterns areadditionally and simultaneously extracted, and output into the picturedecoding apparatus 40 together with the above-described header pattern,the same effects can be attained.

EXAMPLE 2

FIG. 7 is a block diagram of a picture reproduction apparatus in asecond example according to the invention. The second example is mainlydifferent from the first example in that a trick-play mode signal 15 issent to the picture decoding apparatus 40 together with the trick-playcompressed image data 16 in the second example. In the first example,when invalid data is input during the trick play, the picture decodingapparatus retains the image of the previous frame. However, somedecoding apparatus may switch the operation thereof between the processin which the image data of previous frame is retained for theinter-frame encoded frame, and the process in which the image data ofintra-frame encoded frame previously sent is substituted for theinter-frame encoded frame, depending on the error occurrence condition.Accordingly, by sending the trick-play mode signal together with thetrick-play compressed image data, the processing during the trick playcan be surely performed.

The first and second examples are described by way of an apparatus forrecording/reproducing image data compressed by both intra-frame encodingand inter-frame encoding. However, the invention is not limited to thesespecific types of apparatus. Alternatively, such an apparatus can beeasily combined with a recording/reproducing apparatus using intra-frameencoding only.

In the first example, the invalid data is added between the respectiveintra-frame encoded blocks. Alternatively, in the case where intra-frameencoded blocks extracted from several frames of image data are firstcollected in the memory 141 as shown in FIG. 4, and then the intra-frameencoded blocks are successively output into the picture decodingapparatus 40, the same effects can be attained.

In the second example, the trick-play mode signal is fed in addition tothe trick-play compressed image data. Alternatively, the trick-play modesignal may be fed as part of the trick-play compressed image data. Forexample, the trick-play mode signal may be included in the header of thetrick-play compressed image data. However, the invention is not limitedto the specific cases described in the first or second example.

EXAMPLE 3

A picture decoding apparatus in a third example according to theinvention will be described with reference to relevant figures.

FIG. 8 is a block diagram of the picture decoding apparatus in the thirdexample according to the invention. In FIG. 8, a picture decodingsection 4 and a frame memory 5 are identical with the picture decodingsection 4 and the frame memory 5 in the conventional example. Atrick-play control section 6 includes a central processing unit (CPU) 61and a memory 64. FIG. 9 shows an algorithm illustrating the operation ofthe CPU 61.

Hereinafter, the picture coding apparatus with the above constructionwill be described with reference to FIGS. 8 and 9.

The picture decoding apparatus is usually constructed in such a mannerthat, when the decoding of input compressed image data is disabled, onlya part of image which can be decoded is updated, and for the remainingpart of the image which cannot be decoded, the image of the previousframe is retained. Accordingly, for the outputs shown in FIGS. 5 and 6in the first example, only the intra-frame encoded blocks can be updatedwithout modifying the conventional picture decoding apparatus. Thisexample provides a picture decoding apparatus which can reproduce atrick-play mode signal without adding any function to the picturereproduction apparatus.

In FIG. 8, it is assumed that the compressed image data shown in FIGS. 2and 3 is input into the picture decoding section 4. The CPU 61 monitorsa decoding disable flag 63 provided in the variable length decoder 42.The memory 64 stores the information of the header portion which can bevariable-length decoded. If decoding-disabled blocks are detected for apredetermined period, and it is determined that the decoding is disabledbecause a trick play is performed, the CPU 61 operates in accordancewith the algorithm shown in FIG. 9. The positional information ofintra-frame encoded block is extracted from the header informationstored in the memory 64. Next, the CPU 61 outputs a frame memoryinput/output control signal 62, so as to extract the image data ofintra-frame encoded blocks from the compressed image data. The extractedimage data is decoded and then written into the frame memory 5. Theother image data is not updated.

As described above, according to this example, if the input compresseddata is the same as in the normal playback, a picture can be obtained inthe trick play mode because the picture decoding apparatus itselfdetermines if the trick play is performed.

EXAMPLE 4

FIG. 10 is a block diagram of a picture decoding apparatus in a fourthexample according to the invention. In FIG. 10, a picture decodingsection 4 and the frame memory 5 are identical with those in the thirdexample. The fourth example is mainly different from the third examplein that the trick-play control section 6 is constituted only by a CPU inthe fourth example.

In FIG. 10, when the trick play is to be performed, a trick-play modesignal 65 in the second example is input into the trick-play controlsection 6. From the variable length decoder 42, a flag 66 indicatingwhether the input compressed image data is the intra-frame encoded dataor not is input to the trick-play control section 6. The CPU of thetrick-play control section 6 performs the control in such a manner thatonly the intra-frame encoded blocks are written into the frame memory 5,and the remaining blocks of image data are not updated during the trickplay. In this example, when the trick-play mode signal is input, theabove operation is performed. Accordingly, even if the picture decodingapparatus operates to change the retained image depending on the erroroccurrence condition as in the second example, the proper process can beperformed during the trick play.

As described above, only the intra-frame encoded blocks reproduced bythe picture reproduction apparatus are decoded and displayed, and theimage data of the other blocks is not updated. Therefore, it is possibleto obtain a trick-played image with the desired image quality.

In this example, the trick-play mode signal 65 is input. However, theinvention is not limited thereto. Alternatively, if a decoding disableinput which indicates that the decoding of inter-frame encoded blocks isdisabled is input instead of the trick-play mode signal 65, the sameeffects as in this example can be attained. The trick-play mode signal65 may be included in the compressed image data and then input to thepicture decoding section 4 together with the compressed image data.

EXAMPLE 5

FIG. 11 is a block diagram of a picture reproduction apparatus in afifth example according to the invention. In FIG. 11, the picturereproduction apparatus 1 includes a reproducing section 11, a trick-playcontrol section 72, an invalid data producing section 73, and a validdata detecting section 74. Also, a recording medium 2, a recordingsection 3, and a picture decoding apparatus 40 are shown in FIG. 11.FIG. 12 shows the algorithm illustrating the operation of a CPU 721 inthe trick-play control section 72. FIGS. 13A through 13E illustrate theoutputs of the picture reproduction apparatus 1.

The picture reproduction apparatus having the above construction will bedescribed with reference to FIGS. 11, 12, 13A, 13B, 13C, 13D, and 13E.

In FIG. 11, the input image data is compressed by inter-frame encoding.In the recording section 3, the compressed image data is reformattedinto a recording format, and an error correction code is added, similarto the recording section 92 in the conventional example. Then, thereformatted image data with the error correction code is recorded on therecording medium 2. During the normal playback, any error in thereproduced signal is corrected, and the reproduced signal is reformattedinto a decoding format in the reproducing section 11. Thereafter, thereproduced image data is sent to the picture decoding apparatus 40.

When a signal 75 which requires a slow playback at a 1/N speed is input,the reproducing section reproduces the image data by taking a timeperiod multiplied by N, as described in the conventional example. Thereproduced image data is input into the trick-play control section 72and the valid data detecting section 74. In the valid data detectingsection 74, only the valid image data is extracted from the reproducedimage data. The extraction is performed, for example, by utilizing theerror detection result in the reproducing section 11. Alternatively,according to some recording methods, the end of the valid data or theamount of valid data is previously known by a header of the valid data.In such a case, the extraction is performed by utilizing the informationknown from the header.

The CPU 721 of the trick-play control section 72 first stores thereproduced image data into the memory 722. Next, the CPU 721 operates inaccordance with the algorithm shown in FIG. 12. A valid data detectionsignal is input from the valid data detecting section 74, and only thevalid image data is extracted from the reproduced image data stored inthe memory. Next, the valid image data is split into variable-lengthencoding data units. The unit is the minimum unit capable of beingvariable-length encoded. The unit data is output at the same speed as inthe normal playback. In general, the synchronization pattern is added toeach variable-length encoding unit, so that the valid image data caneasily be split into variable-length encoding units by detecting thesynchronization pattern. In the remaining time period other than theperiod in which the variable-length encoding unit data is output, theinvalid data produced in the invalid data producing section 73 is outputinto the picture decoding apparatus 40. In this case, as the invaliddata, a pattern which does not cause the picture decoding apparatus tomalfunction, such as data, that is, all 0 is selected.

FIG. 13A shows the exemplary output during the normal speed playback.FIG. 13B shows the exemplary output during the 1/2 speed playback. Thereproduced image data and the invalid data are alternately output intothe reproduction apparatus by variable-length encoding unit. In general,when the decoding is disabled, the picture decoding apparatus 40 retainsthe previous screen. Accordingly, when the above output is received, thevalid image data of one frame is input for a period of two frames, andthe same screen is retained for the two-frame period. Thus, the slowplayback at the 1/2 speed is realized.

In FIG. 13B, the valid data and the invalid data are alternately outputby variable-length encoding unit. However, the output is not necessarilyperformed alternately. Alternatively, after the valid data consisting ofseveral variable-length encoding units is output, the invalid data ofthe same number of units is output. In such a case, the same effects asin the above example can be attained.

FIG. 13C shows another exemplary output during the 1/2 speed playback.By changing the program for the CPU 121 in the construction shown inFIG. 11, the outputs shown in FIGS. 13C, 13D, and 13E can be realized.In the case shown in FIG. 13C, when the 1/2 slow playback mode signal isinput, the extracted valid image data of one frame and the invalid dataof one frame are output into the picture decoding apparatus. In thisway, the valid data of one frame is reproduced for a unit period of twoframes, and hence the slow playback at the 1/2 speed is realized. When a1/3 speed playback is to be performed, the valid image data of one frameand the invalid data of two frames are output into the picture decodingapparatus. FIG. 13D shows another exemplary output during the 1/2 speedplayback. In this case, the valid image data of two frames and theinvalid data of two frames are alternately output. Also in this way, theslow playback at the 1/2 speed is realized. In addition, a specialeffect in that the picture vibrates by every two frames can be attained.

FIG. 13E shows another exemplary output during the 1/2 speed playbacksimilar to 13C and 13D. In the case shown in FIG. 13E, when the slowplayback mode signal is input, the reproduced image data is split into Mframes. Each of the M split frames is repeated N times, and output intothe picture decoding apparatus. For example, M=1, and the data of oneframe is repeated twice and output, so the picture decoding apparatus 40decodes the frame number in the normal compressed image data, so as towrite the decoded image into a frame memory for image reproduction.Accordingly, when the reproduced image data having the same frame numberis input, the data is written into the same frame memory. That is, thetwo frames which are identical with each other are reproduced for thetwo-frame period, so that the slow playback at the 1/2 speed isrealized.

EXAMPLE 6

FIG. 14 is a block diagram of a picture reproduction apparatus in asixth example according to the invention. The sixth example is mainlydifferent from the fifth example in that the slow playback signal 75 isfed into the picture decoding apparatus 40 together with the imagesignal in the sixth example. In the fifth example, when the invalid datais input during the slow playback, the picture decoding apparatusretains the previous image screen. However, some decoding apparatus mayswitch the operation thereof between the process in which the image dataof previous frame is retained for the inter-frame encoded frame, and theprocess in which the image data of intra-frame encoded frame previouslysent is substituted for the inter-frame encoded frame, depending on theerror occurrence condition. Accordingly, by sending the slow playbackmode signal together with the trick-play compressed image data, theprocessing during the slow playback can be surely performed.

The above examples are described by way of an apparatus forrecording/reproducing image data compressed by both intra-frame encodingand inter-frame encoding. However, the invention is not limited to thespecific type of apparatus. Alternatively, such an apparatus can beeasily combined with a recording/reproducing apparatus using intra-frameencoding only.

In the above examples, only the playback at the 1/2 speed or 1/3 speedis described. Alternatively, the invention can be applied to anyplayback at a 1/N speed.

In the sixth example, the slow playback mode signal is fed in additionto the trick-play compressed image data. However, the invention is notlimited to this specific case. Alternatively, the slow playback modesignal may be fed as part of the trick-play compressed image data. Forexample, the slow payback mode signal may be included in the header ofthe trick-play compressed image data.

EXAMPLE 7

Hereinafter, a picture decoding apparatus in a seventh example accordingto the invention will be described with reference to FIGS. 15 and 16.

FIG. 15 is a block diagram of the picture decoding apparatus in theseventh example according to the invention. A picture decoding section 4and a frame memory 5 in FIG. 15 are identical with those in theconventional example. A trick-play control section 6 is constituted by aCPU. FIG. 16 shows the algorithm illustrating the operation of the CPU.

The picture coding apparatus having the above construction will bedescribed below with reference to FIGS. 15 and 16.

In FIG. 15, a flag 61 indicating the decoded frame number is input fromthe variable length decoder 42. The CPU of the trick-play controlsection 6 operates in accordance with the algorithm shown in FIG. 16.The CPU 6 stores the numbers of frames which have been already decoded.When the same frame is repeatedly decoded, the currently decoded frameis written into the frame memory in which the previously decoded framewith the same number has been stored. If the encoded images with thesame frame number are repeated N times, the writing into the same framememory is performed N times. In this apparatus, as long as the sameframe memory is updated, a displayed image data is output from the sameframe memory. As a result, the playback at the 1/N speed is realized.

The algorithm for the CPU 6 may be changed so that, if the currentlydecoded frame is the same as the previously decoded frame, the framememory is not updated. In such a case, the same operation can also berealized.

Moreover, if it is judged that the decoding operation which is usuallyfinished in one frame takes a time equal to N frames, by the flag 61from the variable length decoder 42, the CPU 6 determines that the 1/Nspeed playback is now performed. Next, if the CPU 6 performs a controlso as to hold the input/output of the frame memory 5 for a period equalto N frames and then to reproduce it, the same effects can be attained.

EXAMPLE 8

FIG. 17 is a block diagram of a picture decoding apparatus in an eighthexample according to the invention. In FIG. 17, a picture decodingsection 4 and a frame memory 5 are identical with those in the seventhexample. The eighth example is mainly different from the seventh examplein that a slow playback mode signal 75 is input into the CPU of thetrick-play control section 6. In the seventh example, the CPU judgesthat the slow playback is being performed by using the information fromthe variable length decoder 42. If the slow playback mode signal isinput as in the eighth example, it is unnecessary for the variablelength decoder to send the frame number to the trick-play controlsection 6. Furthermore, the same operation can be performed. Thetrick-play mode signal 65 may be included in the compressed image dataand then input to the picture decoding section 4 together with thecompressed image data.

Various other modifications will be apparent to and can be readily madeby those skilled in the art without departing from the scope and spiritof this invention. Accordingly, it is not intended that the scope of theclaims appended hereto be limited to the description as set forthherein, but rather that the claims be broadly construed.

What is claimed is:
 1. A picture decoding apparatus for decodingcompressed image data output from a picture reproduction apparatus andreproducing valid image data in either of a normal playback mode or aslow playback mode, the picture decoding apparatus comprising:picturedecoding means for decoding the compressed image data output from thepicture reproduction apparatus; a frame memory for storing the imagedata decoded by the picture decoding means; and trick-play control meansfor performing a control so that a frame number is extracted from thereproduced image data, and, when the extracted frame number is the sameas that of the image data which is input immediately before, the imagedata which is the same as the previous image data is again written intothe frame memory.
 2. A picture decoding apparatus for decodingcompressed image data output from a picture reproduction apparatus andreproducing valid image data in either of a normal playback mode or aslow playback mode, the picture decoding apparatus comprising:picturedecoding means for decoding the compressed image data output from thepicture reproduction apparatus; a frame memory for storing the imagedata decoded by the picture decoding means; and trick-play control meansfor performing a control so that a frame number is extracted from thereproduced image data, and whether the extracted frame number is thesame as that of the image data which is input immediately before or notis determined, and performs a control so that, for the frame number ofthe image data which has been already decoded, the input image data isnot written into the frame memory.
 3. A picture decoding apparatus fordecoding compressed image data output from a picture reproductionapparatus and reproducing valid image data in either of a normalplayback mode or a slow playback mode, the picture decoding apparatuscomprising:picture decoding means for decoding the compressed image dataoutput from the picture reproduction apparatus; a frame memory forstoring the image data decoded by the picture decoding means; andtrick-play control means for performing a control so that, when a timerequired for decoding one frame of compressed image data is equal to(N-1) frames or more or equal to N frames or less (N is a naturalnumber), the contents of the frame memory are retained for a period of Nframes or more.
 4. A picture decoding apparatus for decoding compressedimage data output from a picture reproduction apparatus and reproducingvalid image data in either of a normal playback mode or a slow playbackmode, the picture decoding apparatus comprising:picture decoding meansfor decoding the compressed image data output from the picturereproduction apparatus; a frame memory for storing the image datadecoded by the picture decoding means; and trick-play control means forperforming a control so that, when a slow playback mode at a 1/N speed(N is a natural number) is input, the contents of the frame memory areretained for a period of N frames or more.
 5. A picture decodingapparatus comprising:picture decoding means for decoding compressedimage data; a frame memory for storing the decoded image data; andtrick-play control means for, when a control signal is input, performinga control so that an intra-frame encoded portion is written into theframe memory, and the contents for the remaining portion other than theintra-frame encoded portion are not updated.
 6. A picture decodingapparatus according to claim 5, wherein the control signal is a decodingdisable signal which is input during a predetermined period.
 7. Apicture decoding apparatus according to claim 5, wherein the controlsignal is a trick-play mode signal.